when I call the image why does not appear?

a=uigetfile();
filename=a;
setappdata(0,'filename',filename);
a=imread(a);
axes(handles.axes1);
imshow(a);
setappdata(0,'a',a);
setappdata(0,'filename',a);
plot(handles.axes1,'a'); 

[Rik]

Why exactly are you using this code? Why do you expect plot to display an image?

If you have trouble with Matlab basics you may consider doing the Onramp tutorial (which is provided for free by Mathworks).

Answer 1

[Image Analyst]

You don't need to do anything with appdata. Simply do this:

% Have user browse for a file, from a specified "starting folder."
% For convenience in browsing, set a starting folder from which to browse.
startingFolder = pwd;  % or 'C:\wherever';
if ~isfolder(startingFolder)
    % If that folder doesn't exist, just start in the current folder.
    startingFolder = pwd;
end
% Get the name of the file that the user wants to use.
defaultFileName = fullfile(startingFolder, '*.*');
[baseFileName, folder] = uigetfile(defaultFileName, 'Select a file');
if baseFileName == 0
    % User clicked the Cancel button.
    return;
end
fullFileName = fullfile(folder, baseFileName)
% Read image into an array.
rgbImage = imread(fullFileName);
% Display the image.
imshow(rgbImage, []);

[Image Analyst]

See my Image Segmentation Tutorial in my File Exchange:

Image Analyst's File Exchange

It's a generic, general purpose demo of how to threshold an image to find blobs, and then measure things about the blobs, and extract certain blobs based on their areas or diameters.